The present invention relates to an arrangement for reducing a rotational speed of a rotating member. The arrangement comprises a first and second pressure member arranged at a distance from each other and on opposite sides of the rotating member. The first and second member are movable relative to each other between a retracted position and a forward position engaging the rotating member. The invention is particularly suitable for application in a hydraulic disc brake in which the pressure members are pressed against opposite faces of a brake disc to provide frictional resistance to its rotation.
The arrangement comprises an adjustment device comprising a friction means forming a friction joint with one of said pressure members for maintaining a position relative to one another provided a maximum friction force is not exceeded. The arrangement further comprises a spring means acting on the friction means for separating the pressure members after having been compressed. The spring means has a gradually increasing spring force between a non-compressed state and a totally compressed state.
The invention will below, in a non-limiting example, be explained for a brake. The first pressure member forms a brake piston. The friction means forms the friction joint with the piston. The second pressure member forms a stationary member forming a mechanical stop. During each application of the brake, the piston moves forwardly, the friction means moving with it, until the opposite faces of the brake piston and the stationary member are in frictional engagement with the brake disc. The spring means is compressed during this movement. When the brake piston is released from brake pressure, it is urged away from the face of the brake disc by the spring means acting on the friction means. An automated return function is thereby achieved. Further, the piston is movable to a displaced position relative to the friction means when a maximum friction force of the friction joint is exceeded. In this way, the clearance is maintained substantially constant despite wear.
In U.S. Pat. No. 3,085,663, an automatic adjustment device for a brake is disclosed. The device is arranged in a recess in a brake piston. The friction means is formed by a close-coiled helical spring in frictional engagement with the peripheral wall of the recess. The spring means is formed by a dished disc-type washer arranged beside the helical spring. During each application of the brake, the disc-type spring washer is compressed to a flat condition. One disadvantage with this arrangement is that the spring effect of the washer will be deteriorated, due to cracks etc, after a number of brake applications.
It is desirable to achieve an arrangement for reducing a rotational speed of a rotating member with a longer life in relation to earlier known designs. It is also desirable to achieve a compact design minimizing the number of articles necessary.
According to an aspect of the present invention, an intermediate spring force value of the spring means, which corresponds to compression of the spring means to an extent less than said totally compressed state, equals a maximum friction force of the friction joint so that the friction means is forced to move relative to the pressure member, with which it forms the friction joint, when said maximum friction force is exceeded. Thus, the spring force of the spring means is balanced to the friction force of the friction joint.
Due to the fact that the spring means will not, at any time, be compressed to the totally compressed state, it will not be subjected to as large loads as prior art devices and thus have a longer life. Further, the automatic return function and constant clearance is achieved in one single apparatus, which creates conditions for a cost-efficient production and installation. More specifically, the adjustment device may be pre-mounted.
According to a preferred embodiment, the friction means is at least partly arranged in an opening in the pressure part and that an outer surface of the friction means and a peripheral wall of the opening have a complementary design for forming the friction joint. This design creates further conditions for a cost-efficient production and installation. Only one hole is required in one of the pressure members. According to a further development of the embodiment above, the spring means has a smaller outer diameter than the outer diameter of the friction portion. In this way, the first pressure part may be moved to a position where there is an overlap between the first pressure part and the spring means seen in the radial direction.
According to a further preferred embodiment, the spring means comprises a plurality of dished disc-type washers and that at least two of the washers extend in different directions. By virtue of this design, a sufficient spring effect is achieved in a space-efficient way.
According to a further preferred embodiment, the adjustment device comprises an elongate support portion and the friction means is arranged for movement relative to the support portion in its longitudinal direction. This creates conditions for a compact and cost-efficient design.
Further preferred embodiments and advantages will be apparent from the following description.